The IEEE 802.15.4 media access control (MAC) system is the most representative technology for realizing a real-time high reliability service in a low power based wireless sensor network (WSN) system. The IEEE 802.15.4 MAC system constitutes a network having a tree structure starting from a personal area network is coordinator (PNC), allocates an independent active duration to each node according to a scheduling method, and supports communication during the corresponding active duration.
When each node transmits a beacon, the active duration is referred to as an outgoing superframe duration (OSD). When a parent node transmits a beacon in the tree structure, the active duration is referred to as an incoming superframe duration (ISD). OSDs of adjacent nodes are scheduled not to overlap temporally in order to avoid beacon collisions.
A node basically receives data using carrier sense multiple access with collision avoidance (CSMA-CA) during a contention access period (CAP) in order to communicate with a parent node. When a node desires channel access in a beacon based operating mode, a child node may use scheduling based channel access during a designated time slot. In more detail, nodes capable of performing one-hop communication with the PNC receive guaranteed time slots (GTS) and perform scheduling data communication. To this end, nodes capable of directly communicating with the PNC indicate that they require independent time by sending a GTS request frame, and the PNC transmits whether to allocate time by using a beacon.
However, since the IEEE 802.15.4 MAC system uses a single frequency in a duration of using a link, it is vulnerable to an interference signal having the same radio frequency (RF) band, and difficult to variably schedule a communication link bandwidth. Furthermore, since the IEEE 802.15.4 MAC system uses a tree topology, it is possible to communicate between a parent node and a child node but impossible to communicate between child nodes.